Transmission line



Oct. 29, 1940. L. KRUGEL 2,219,653

TRANSIISSION LINE Filedvnec. 1e, 193s ATTORN EY I BY Patented Oct. 29, 1940 UNITED STATES TRANSLIIS SION LINE Lothar Krgel, Berlin, Germany, assignor to Telefunken Gesellschaft fur Drahtlose Telegraphie m. b.- H., Berlin, Germany, a corporation of Germany Application December 16, 193s, serial No. 116,134

In Germany December 16, 1935 z claims.

The present invention relates to a cable for conducting high-frequency energy, particularly decimeter waves.

A great many different constructions oi' highfrequency cables are known and have been proposed. The transmission cable system best known is that which `employs wires especially concentric wire lines.

Figure y1 shows in principle such a high-frequency cable. There extends along the axis of the metal tube A, the inner conductor B held in the axial position by spaced insulating rings R. Since the insulating spacer rings R may cause losses in the cable through imperfect insulation, a

great many constructions and insulating ma'- terials have been proposed for these spacers. For -this purpose, ceramic, organic and other insulating materials are employed in suitable shapes. 'I'hus for instance, instead of forming the spacers as rings, the spacers may be so formed that they can be helically Wound about the inner conductor in the manner of a band, or pearl string.

Although the losses appearing in the cable can be decreased by these measures, it is not possible to eliminate the losses completely. 'I'he losses are produced primarily by the ohmi'c resistance in the conductors, and through transition resistances in the spacers. If such cables are employed for the transmission of wide speech frequency or television frequency bands, magnetic and, apparently also, electrical disturbances may act on the cable from the outside, and which can likewise be considered losses.

Therefore, it has been proposed that ultra short waves be transmitted from one place to a second place by way of radiation. The present invention is not concerned with providing a directive eiect for the radiation in free space, but rather, transmission oi' Waves is to be eii'ected from one plate 40 to another by radiation in metallic tubes.

Figure -2 shows schematically such an arrangement. A metal tube Sch having any desired diameter is placed between the place of transmission S and the place of reception E. The dipole- D1 is connected to the transmitter and the dipole Dz to the receiver. The energy is transmitted from S to E through radiation in the direction indicated by the arrows, whereby thev radiation losses through total reflection on the inside or the tube are avoided. Similar methods for the transmission oi' light are known; in place of a tube,

quartz sheets are used in this case in which likewise the total reflection of the light occurs. It should be noted, however, that in this case also, the energy sent through the cable at the place oi transmission does not arrive in toto at the place of reception, since losses occur at the tube walls through incomplete reiiection.

Now in order that the desired eiects of the energy transmission occur, it is necessary that the 5 polarization oi' the waves employed should extend at right angie to the axis of the tube, since in the direction of polarization, i. e., therefore, in the direction of the axis of a dipole, radiation does not occur. (The term direction of polarization 10 is meant to designate the direction of the electrical ileld vector.)

In accordance with the invention, the energy of very short waves, more especially decimeter waves, is likewise transmitted within a metal tube, 15 but the direction oi.' polarization of the waves is parallel to the axis of the tube.

In the drawing l Figs. 1 and 2 show two wave transmission structures and are given for purpose of exposi- 20 tion;

Figs. 3, 6 and 7-illustrate different embodiments of the invention; and

Figs. 4 and 5 show ileld distribution curves for tubular structures in accordance with the inven- 25 tion having dilerentradii.

The functioning of the invention will be discussed with reference to Figures 3, 4 and 5. Figure 3 shows schematically an energy transmission system in accord-ance with the invention. At the 30 place of transmission there is arranged in the axis of the metal tube L the dipole D3 connected to the transmitter S. The dipole D4 whichis likewise arranged coaxially, is connected to the receiver E.

The coaxial arrangement of the radiators ap- 35 pears at iirst contradictory since, as mentioned above, radiation does not occur in the axis of the dipole. But hereby a new effect occurs.

In fact when measuring the distribution of the energy within the interior of the tube L, it is 40 found that the eld distribution for a deilnite cross section plane of the tube remains, as regards value, substantially constant over the en-tire length of the tube. This phenomenon becomes particularly pronounced if the radius of the tube 45 and the wave length employed have a lcertain relation.

In Figures 4 and 5 the curves of fleldidistributions are shown as obtained for twodifferent radii of the tube. In Figure '4, item Z designatesl the 50 'cylindrical wall of the tube, and St the 4radiator connected to the generator G. The curve (t, in dot and dash lines, shows above the diameter D the values of the electric field component as function of the diameter. If at the same wave length V55 wherein R indicates the radius of the tube, and a the wavelength of the radiation. Kr indicates the zero point of the Bessel function and can assume the valuesto 2.40; 5.52; 8.65; 11.79.

As seen from the above, by means of the arrangement according to the invention, the interior of the tube L (Figure 3) is excited in space resonance. Practically in all points of the inner space the same ileld strength exists, so that the energy sent from the dipole D: at the place of transmission, can be obtained again at the place of reception at the dipole D4 substantially without loss.

The cable according to the invention can be used in various ways. It is particularly suited for the bridging of very great distances, whereby eventually tubular lines can be used that have been provided for other purposes. In this connection there may be thought of gas-oil-and water lines. With such an arrangement another advantage will be obtained. It is known that the wavelengths of an oscillation relate to each other in two different media in accordance with the inverse proportion of the roots of the dielectric constants. If the cylindrical tube is filled with water for instance (dielectric constant 81) then in the water the Wave length is 376 of that in air. This signies that the cylinder filled with water requires only a diameter equal to $6 of that of the cylinder lled with air. Inversely, for a given tube, the wave length may be nine times longer 45 where the cable is lled with water.

In general the following relationship exists:

a: Kr

5o wherein e is the dielectric constant of the medium existing in the interior of the cable.

For further elucidation an example in figures will be given. There is assumed a tube having a free width of 40 cm. (R=20 cm.). In accordance 55 with the formula given above, across such a tube when using space resonance, the following waves can be sent: 7\1=52.2; M=22.8; .a=14.5; 7\4=1O.65 cm. Obviously all waves may be used simultaneously so that the tube can be used in a quadruple G0 way as' cable.

If the cable tube is filled with water the said waves can be sent out across a tube being only 4.44 cm. in diameter, or waves can be sent across a tube of 40 cm. diameter which are. nine times 65 longer than those given.

If in an existing tube, high-frequency is to be transmitted, for instance, from the center to one of the two ends, it is advisable to have only the part of the cable necessary for the transmission,

70 excited in space resonance. The part not used will then be electrically separated; this may be done for instance by inserting a metal plate in the cable. Such an arrangement is schematically represented in Figure 6. The radiator St con- 75 nected with the generator G is to send energy into the cable tube designated by M. 'Ihe receiver. not shown, is assumed to be located at the right of the gure. In this case it is not necessary to excite the -tube extending further to the left, and therefore, the metal plate P is provided which closes up the Icable electrically. If a tube serving for other purposes is Ialso used for transmitting high-frequency energy, the cover plate P must, of course, not consist of a solid metal, otherwise the passage of water for instance would be blocked. In this case the cable is electrically closed up in accordance with the invention by means of a wire net or the like. The distance between the cover plates and the radiators is suitably so chosen that the field intensity appearing in the resonance space is a maximum. The most favorable distance will advisably have to be decided for each case by experiment.

Since the direction of polarization of the transmitted waves is to be in the axis of the cable, so as to obtain the effect of the space resonance, it is necessary that in case of cable bends, the energy be carried around the bend. Figure 'l shows schematically a construction of such a bent line. The straight parts of the cable are electrically closed up ahead of the bend of the tube by the plates P1 and Pn. (These plates may, of course, be wire nets or screens.) The energy is transmitted from the one straight part to the other one of the tube in that the energy is received by the receiving dipole ED and is again radiated by a transmission dipole SD connected to ED across an ordinary energy line. In the circuit of the energy line connecting the two dipoles, an amplifier V may eventually be inserted, as shown.

There also is a possibility that the diameter of the cable may greatly vary at a place for instance where two different tube sections are joined with each other. In this case it is necessary, in order to attain resonance, that the wave length employed in the two cable sections be changed. 'I'his can be accomplished in accordance with the scheme shown in Figure '7. .In this case the energy received by ED would be detected in V. -The useful modulation now will likewise be used in V as modulation for a new carrier, whose wave length is suitably chosen in accordance with the above equation for the following cable section.

Only one example will be given as field of application of the cable according to the invention. For the planned network of television transmitters, a cable system distributed throughout Germany is required which, without essential losses, connects the individual transmitters with the central transmitter. A cable according to Figure 1 with styroex insulation is soon to be laid out between Berlin and Mount Brocken (see E. T. Z.

1935, volume 46, page 1 245 and following).

When using the cable according to the invention, only single tubes need be laidout between the individual places. The messages to be transmitted now are superimposed on a wave adapted to the diameter of the tube line. and with the wave thus modulated the tubular cable is energized in space resonance. Magnetic and electrical disturbances coming from the outside do not seriously affect the system in view of the short wave used as carrier. Likewise, losses such as are always present in an energy transmission according to Figure 2 owing to the reflection losses, do not appear or only to a very small extent in View of `the Space resonance.

It is possible to transmit any desired number of messages across such a cable, since the carrier wave can be modulated in any desired manner;

if desired, also several carriers may be used at the same time. 'I'hus it is readily conceivable that the high-frequency line can replace present and known message transmission stations. Ordinary cables, Whether they are below or above ground, are susceptible of disturbances. 'Ihe same is true in case of Wireless connections which are endangered primarily by atmospheric iniluences. In the cable according to the invention, all these drawbacks are not encountered as already explained above.

I claim:

1. In combination, a. transmission line for conducting ultra-short waves comprising a hollow tube having a suitable dielectric medium in the interior thereof, a dipole antenna for transmitting through the interior of said tube waves whose electric eld component is parallel to the axis of said tube, the dimensions of said tube substantially satisfying the equation ...K-r. 2x1/2 where Kr is the zero order of the Bessel function,

R the radius of the tube, 7i the length of the communication wave, and e the dielectric constant of the medium within said tube. and a dipole receiv-f" ing antenna in the interior of said hollow tube,

both said dipole antennas having their axes in the axis of said hollow tube.

2. In combination, a transmission line for conducting ultra short waves comprising a bent hollow tube having straight portions on both sides of -the bend thereof, means for transmitting through the interior of said tube waves whose electric field component is parallel to the axis of said tube, the radius of said tube having a predetermined relation to the wavelength, a dipole antenna in each straight portion in the axis of said tube, a metal plate in said tube spaced from each antenna for electrically separating said antennae from the portion of the tube comprising the bend, and an electrical circuit for transferring energy from one of said antennas to the other, the distance between said plates and their respective antennae being so chosen that the field intensity in the interior of the hollow tube assumes maximum values. I

LoTHAR KRGEL. 

